Cryopumps, currently available, are typically used in equipment for the manufacture of integrated circuits and other electronic components, as well as for the deposition of thin films in a variety of consumer and industrial products. The cryopumps are used to create a vacuum by freezing or pumping out gases in a work environment. Refrigerators employed by the cryopumps for pumping out gases may be an open or a closed-cycle, cryogenic refrigerator. The most common refrigerator used is a two-stage cold finger, closed-cycle refrigerator.
The design concept of the cryopumps employed in industry is similar. Typically, the cold end of the second stage, which is the coldest stage of the two-stage refrigerator, is connected to a primary pumping surface. The primary pumping surface operates in a temperature range of 4.degree. to 25.degree. K. The first stage of the two-stage refrigerator is connected to a radiation shield which surrounds the primary pumping surface. The spacing between the primary pumping surface and the radiation shield must be sufficient to permit unobstructed flow of low-boiling temperature gases from a vacuum chamber created by the shield to the primary pumping surface. The radiation shield typically operates in a range of 70.degree. to 140.degree. K. Separating the evacuation chamber and the radiation shield is a frontal array, which also serves as a radiation shield for the primary pumping surface. The frontal array is typically cooled to 110.degree. to 130.degree. K. by thermally coupling it to the radiation shield.
In operation, high boiling point gases, such as water vapor, are condensed on the frontal array. Lower boiling point gases pass through that array and into a volume within the radiation shielding, where they condense on the primary pumping surface. An absorbent, such as charcoal, is typically placed adjacent to the primary pumping surface and is operated at a temperature of that surface to absorb gases which have very low boiling point temperatures and are not condensed on the primary surface.